Development of a recombinant vaccine against foot and mouth disease utilizing mutant attenuated Listeria ivanovii strain as a live vector.

The drawbacks of conventional inactivated Foot and Mouth Disease (FMD) vaccine, such as escaping of the virus during manufacture processes prompted researchers to explore novel types of vaccine to overcome these disadvantages. Listeria ivanovii (LI) is an intracellular microorganism that possesses immune-stimulatory properties, making it appropriate for use as a live bacterial vaccine vector. The Foot and mouth disease virus (FMDV) VP1 protein is the most immunogenic part of FMDV capsid, it has most of the antigenic sites for viral neutralization. The expression of antigen gene cassette in vitro was confirmed by Western blot analysis. Mice were able to eliminate LI△actAplcB-vp1 from the liver and spleen within few days revealed a safety of the candidate vaccine. Two doses of LI△actAplcB-vp1 with 14 days of interval were injected into mice. High levels of specific IgG antibodies and CD8+ and CD4+ T cells secreted cytokines including IFN-γ, TNF-α and IL-2 against FMDV-VP1 were achieved. Based on the obtained results, LI△actAplcB-vp1 candidate vaccine utilizing Listeria ivanovii as a live vector-based vaccine could enhance a specific cellular and humoral immune responses against the inserted FMDV-vp1 heterologous genes. LI△actAplcB-vp1 candidate vaccine could be a modern tool to overcome the disadvantages of the traditional inactivated FMD vaccine.

Expression of the VP1 protein of FMDV integrated chromosomally with mutant Listeria monocytogenes strain induced both humoral and cellular immune responses.

Live vector-based vaccine is a modern approach to overcome the drawbacks of inactivated foot-and-mouth disease (FMD) vaccines such as improper inactivation during manufacture. Listeria monocytogenes (LM), an intracellular microorganism with immune-stimulatory properties, is appropriate to be utilized as a live bacterial vaccine vector. FMDV-VP1 protein has the capability to induce both cellular and humoral immune responses since it is considered the most immunogenic part of FMDV capsid and has the most of antigenic sites for viral neutralization. The codon-optimized vp1 gene was ligated to the integrative pCW702 plasmid to construct the target cassette. The antigen cassette was integrated successfully into the chromosome of mutant LM strain via homologous recombination for more stability to generate a candidate vaccine strain LM△actAplcB-vp1. Safety evaluation of recombinant LM△actAplcB-vp1 revealed it could be eliminated from the internal organs within 3 days as a safe candidate vaccine. Mice groups were immunized I.V. twice with the recombinant LM△actAplcB-vp1 at an interval of 2 weeks. Antigen-specific IgG antibodies and the level of CD4+- and CD8+-specific secreted cytokines were estimated to evaluate the immunogenicity of the candidate vaccine. The rapid onset immune response was detected, strong IgG humoral immune response within 14 days post immunization and augmented again after the booster dose. Cellular immunity data after 9 days post the prime dose indicated elevation in CD4+ and CD8+ secreted cytokine level with another elevation after the booster dose. This is the first report to explain the ability of attenuated mutant LM to be a promising live vector for FMDV vaccine.